Exoplanet characterization is one of the main foci of current exoplanetary science. For super-Earths and sub-Neptunes, we mostly rely on mass and radius measurements, which allow us to derive the mean density of the body and give a rough estimate of the bulk composition of the planet. However, the determination of planetary interiors is a very challenging task. In addition to the uncertainty in the observed fundamental parameters, theoretical models are limited owing to the degeneracy in determining the planetary composition.
 We aim to study several aspects that affect the internal characterization of super-Earths and sub-Neptunes: observational uncertainties, location on the M-R diagram, impact of additional constraints such as bulk abundances or irradiation, and model assumptions.
 We used a full probabilistic Bayesian inference analysis that accounts for observational and model uncertainties. We employed a nested sampling scheme to efficiently produce the posterior probability distributions for all the planetary structural parameter of interest. We included a structural model based on self-consistent thermodynamics of core, mantle, high-pressure ice, liquid water, and H-He envelope. 
 Regarding the effect of mass and radius uncertainties on the determination of the internal structure, we find three different regimes: below the Earth-like composition line and above the pure-water composition line smaller observational uncertainties lead to better determination of the core and atmosphere mass, respectively; and between these regimes internal structure characterization only weakly depends on the observational uncertainties. We also find that using the stellar Fe/Si and Mg/Si abundances as a proxy for the bulk planetary abundances does not always provide additional constraints on the internal structure. Finally we show that small variations in the temperature or entropy profiles lead to radius variations that are comparable to the observational uncertainty. This suggests that uncertainties linked to model assumptions can eventually become more relevant to determine the internal structure than observational uncertainties.

How to cite: Fernandez Otegi, J., Dorn, C., Helled, R., Bouchy, F., Haldemann, J., and Alibert, Y.: Impact of the measured parameters of exoplanets on the inferred internal structure., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4617, https://doi.org/10.5194/egusphere-egu21-4617, 2021.

Introduction. Post-accretionary impact bombardment is part of planet formation and leads to localized, regional [e.g., 1-3], or even wholesale global melting of silicate crust [e.g., 4]; less intense bombardment can also create hydrothermal oases favorable for life [e.g, 5]. Here, we generalize the effects of late accretion bombardments to extrasolar planets of different masses (0.1-10M_⊕). One example is Proxima Centauri b, estimated at ~2× M_⊕ [6]. We model a 0.1M_⊕ “mini-Earth”and “super-Earth” at 10M_⊕, the approximate upper limit for a “mini-Neptune” [7]. Output predicts lithospheric melting and subsurface habitable volumes.

Methods. The model [1,2] consists of (i) stochastic cratering; (ii) analytical thermal expressions for each crater [e.g., 8,9]; and (iii) a 3-D thermal model of the lithosphere, where craters cool by conduction and radiation.

We analyze impact bombardments using our solar system’s mass production functions for the first 500 Myr [10]. Surface temperatures and geothermal gradients are set to 20 °C and 70 °C/km [2]. Total delivered mass for Earth is 7.8 × 10²¹ kg, and scaled to other planets based on cross-sectional areas, with 1.7 × 10²¹ kg for mini-Earth, 1.2 × 10²² kg for Proxima Centauri b, and 3.6 × 10²² kg for super-Earth. The impactors' SFD is based on our main asteroid belt [11]. Impactor and target densities are set to 3000 kg m^-3 and planetary bulk densities are assumed to be 5510 kg m^-3, omitting gravitational compression [7]. Impactor velocity was estimated at 1.5 × v_esc for each planet, with 7.8 km s^-1 for mini-Earth,  16.8 km s^-1 for the Earth, 21.1 km s^-1 for Proxima Centauri b, and 36.1 km s^-1 for super-Earth.

Results. We assume fully formed crusts, so melt volume immediately increases due to impacts. Super-Earth reaches a maximum of ~45% of the lithosphere in molten state, whereas mini-Earth reaches a maximum of only ~5%.  This is due to much higher impact velocities and cratering densities on the super-Earth compared to mini-Earth. We also show the geophysical habitable volumes within the upper 4 km of a planet’s crust as the bombardment progresses. Impacts sterilize the majority of the habitable volume on super-Earth; however, due to its large total volume, the total habitable volume is still higher than on other planets despite the more intense bombardment in terms of energy delivered per unit area.

References: [1] Abramov, O., and S.J. Mojzsis (2009) Nature, 459, 419-422. [2] Abramov et al. (2013) Chemie der Erde, 73, 227-248. [3] Abramov, O., and S. J. Mojzsis (2016) Earth Planet Sci. Lett., 442, 108-120. [4] Canup, R. M. (2004) Icarus, 168, 433-456. [5] Abramov, O., and D. A. Kring (2004) J. Geophys. Res., 109(E10). [6] Tasker, E. J. et al. (2020). Astronom. J., 159(2), 41. [7] Marcy, G. W. et al. (2014). PNAS, 111(35), 12655-12660. [8] Kieffer S. W. and Simonds C. H. (1980) Rev. Geophys. Space Phys., 18, 143-181. [9] Pierazzo E., and H.J. Melosh (2000). Icarus, 145, 252-261. [10] Mojzsis, S. J. et al. (2019). Astrophys. J., 881(1), 44. [11] Bottke, W. F. et al. (2010) Science, 330, 1527-1530.

How to cite: Mojzsis, S. J. and Abramov, O.: Thermal consequences of impact bombardments to silicate crusts of terrestrial-type exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13084, https://doi.org/10.5194/egusphere-egu21-13084, 2021.

Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior.
We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere.

To study the coupled star-planet evolution, we analyse the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculate different rotation evolutionary tracks for Proxima Centauri and investigate the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely higher in the past. 
We apply an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, i.e. different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. 
We use a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions we chose randomly selected values. We take into account heating in the interior due to variable radioactive heat sources and latitute- and radius-dependent induction heating, and compare the heating efficiency to tidal heating.

Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin (see Fig. 1). This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet would not have been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. We furthermore find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior.

Fig 1: Local induction heating and resulting temperature variations compared to a simulation without induction heating after 1 Gyr of thermal evolution for an example rocky planet of 1.8 Earth masses with an iron content of 20 wt-%.

How to cite: Noack, L., Kislyakova, K., Johnstone, C., Güdel, M., and Fossati, L.: Interior heating and outgassing of Proxima Cen b: Identification of critical parameters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2299, https://doi.org/10.5194/egusphere-egu21-2299, 2021.

The large iron core of Mercury and the low iron contents on the surface inferred from MESSENGER data suggest the presence of a magma ocean after accretion. We modeled the lifetime of an early Hermean magma ocean as well as the structure and loss rates of an atmosphere that is sourced by degassing. We use a large range of initial conditions including several bulk compositions associated with varying degrees of differentiation, the inclusion of carbon and hydrogen degassing volatiles such as CO2 and H2O, as well as considering a larger proto-Mercury size. After obtaining the magma ocean lifetime and volatile vapor pressures, the result is passed on to further models to obtain metal oxide vapor pressures, a complete atmospheric photochemical speciation and ultimately the mass loss rate of the atmosphere.

We show that magma ocean cooling times are sensitive to the size of the planet and the efficiency of radiative heat transfer in the atmosphere. A volatile-free proto-Mercury radiating as a blackbody with its present-day size would cool down within 400 years from an assumed initial surface temperature of 2500 K to an early crust formation threshold of 1500 K. In contrast it takes 9000 years for a volatile rich proto-Mercury with a greenhouse atmosphere and a mantle size representing Mercury before the occurrence of a mantle stripping event. Volatile-rich cases reach massive atmosphere pressures, whereas volatile-free cases are dominated by Si, Na, K, Mg, and Fe species degassed from the magma ocean and end up at a maximum pressure of 0.1 bar at 2500 K. There is however only a small difference in the atmospheric extent, as the absence of volatile species in the thin metal oxide atmosphere causes it to become extended to a degree, where an upper atmosphere height comparable to the volatile cases is reached. In terms of mass loss we found that upper atmospheric loss due to photoionization is highly efficient in the environment of a young Sun, ionizing 100% of the particles reaching Mercury’s exosphere. This leads to loss rates of up to 10⁶ kg/s, which are however diffusion limited by the supply from the homopause, reducing them by 2-3 orders of magnitude. In regards to Na and K loss, we found that a thin, volatile-free atmosphere is most efficient with its extended structure allowing for large loss rates as well as the high Na and K mixing ratio.

How to cite: Jäggi, N., Gamborino, D., Bower, D. J., Sossi, P., Wolf, A., Vorburger, A., Oza, A. V., Wurz, P., and Galli, A.: Early Mercury’s magma ocean atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4011, https://doi.org/10.5194/egusphere-egu21-4011, 2021.

One of the fundamental questions for planetary science is how surfaces of other planets similar to the rocky bodies in our solar system look like. What is the rock structure like? Will there be water? Are there any active atmospheric cycles? How can these different conditions be detected?

The current space missions and ground based instruments allow the detection of specific gas species and some cloud compositions in atmospheres of giant exoplanets. With instruments  installed in the near future and space crafts currently being build or planned, these kind of observations will be available for planets with smaller sizes and an overall rocky composition. We aim to further understand the connection of the conditions of the upper atmosphere with the conditions on the crust of the planet (temperature, pressure, composition).

Our equilibrium chemistry models allow us to investigate the expected crust and near-crust-atmosphere composition. With this, we investigate the conditions under which liquid water is actually stable at the surface of a planet and not incorporated in hydrated rocks. Based on this crust - near-crust-atmosphere interaction we build an atmospheric model, which allows us to investigate what kind of clouds are stable and could be present in atmospheres of rocky exoplanets. This allows us to predict what clouds on other planets could be made of. Potential detection of cloud condensates and the high altitude gas phase can constrain the overall surface conditions on those planets. 

How to cite: Herbort, O., Woitke, P., Helling, C., and Zerkle, A.: From clouds to crust - Cloud diversity and surface conditions in atmospheres of rocky exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9745, https://doi.org/10.5194/egusphere-egu21-9745, 2021.

Introduction: Small cones are common on Mars. Many cones form subparallel chains several kilometers in length. Their origin is discussed in many papers, however, the mechanism of their formation is not explained [1].

In the present paper, we deal with a small region in Chryse Planitia ( ~38^o13′ N and ~319^o25’ E). The region is covered by lacustrine deposits.

    On Mars, chains of small cones occupy vast areas. Therefore, we try to explain the existence of the chains by specific conditions on Mars. We focus on the hypothesis connecting the formation of cones with the loss of water from the regolith due its instability. See e.g. [1], [2], [4], [5].

Mechanism of cones formation: We consider 3 mechanisms of cone formation: (i) a grains’ ejection, (ii) from mud or fluidized sand and (iii) explosive formation. The (iii) and (ii) are possible with additional heat sources only.

    Assuming that only heat of melting was used for vaporization, then only ~13% of liquid water will be vaporized, If the outgassing effect is to be regolith without water, then there must be also other heat sources. Therefore we consider two coexisting factors required for cones formation: (1) the presence of water in the regolith and (2) some additional heating, e.g. magma intrusion.

    The formation of a chain of cones is possible in two situations:

(a) above a linear structure containing water and areal heating. Outcrops of aquifers could serve as linear sources of volatiles.

(b) above a linear source of magmatic heat and the areal aquifer. A dike could serve as linear source of heat.

Conclusions and future plans;

1) Considered cones could be a result of outgassing of regolith due to pressure drop.

2) Subparallel chains of cones were formed along the outcrops of volatile-rich sediments.

3) Numerical modeling indicates that small magma intrusions may not be enough for completely degassing some aquifers.

Acknowledgments: This study was supported by statutory project of Institute of Geophysics of University of Warsaw. We are also grateful to prof. W. Kofman and dr. J. Ciążela for their remarks.

References

[1] Fagents, S., Thordarson, T., (2007) The Geology of Mars: Evidence from Earth-Based Analogs, ed. Mary Chapman. Cambridge Univ. Press. [2] Brož,, et al. (2019) JGR: Planets. 124, 703–720. [3] Rotto, S., Tanaka, K. L. (1995) Geologic/ geomorphologic map of the Chryse Planitia: region of Mars. USGS. [4] Barlow, N.G. (2010) GSA Bulletin (2010) 122 (5-6): 644–657. [5] Brož, P., et al. (2020) Nature Geoscience. 13, 403–407.

How to cite: Czechowski, L., Zalewska, N., Zambrowska, A., Ciazela, M., Witek, P., and Kotlarz, J.:  The mechanisms of formation of some small cones in Chryse Planitia on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15422, https://doi.org/10.5194/egusphere-egu21-15422, 2021.

Mercury is characterized by a globally low reflectance associated with remarkably low iron contents. Among several proposed hypothesis, to date, the most convincing explanation of the low reflectance of Mercury invokes mixing of an ancient graphite-rich crust with overlying volcanic materials via impact processes and/or assimilation of carbon into rising magmas during secondary crustal formation (e.g. Peplowski et al.2016). Even though until now graphite has not been directly observed, there are strong evidences suggesting its presence on Mercury’s surface (e.g. Denevi et al.2009; Peplowski et al.2011). The actual presence of graphite within Mercury soil may have several implications, e.g. on the late accretion history of Mercury (Hyodo et al.2021; Murchie et al.2015) or on hollow formation (Blewett et al.2016). Moreover, silicates are often associated to carbon phases in some achondrites (e.g. ureilite, Nestola et al.2020, and references therein). Evaluating in a systematic way the effect of graphite on visible and near-infrared spectroscopy of mafic mineral absorptions is thus of interest to improve our understanding of Mercury remote sensing data, and to make progress in our capability to associate carbon-rich stony meteorites to their parent bodies. Mixing graphite with silicate materials is thought to basically decrease the contrast of reflectance spectra of these materials (Murchie et al.2015). Nevertheless, systematic works addressing the influence of graphite-silicate mixtures on their reflectance spectra are still lacking. Here we mixed microcrystalline graphite with a suite of silicate materials and measured their VNIR reflectance spectra. We selected three silicate end-member compositions, namely: 1) a synthetic glass with chemical composition close to the one inferred for of the volcanic products emplaced in the Mercury’s northern volcanic plains (Vetere et al.2017), 2) a Mg-rich Gabbronorite with FeO < 3% (Secchiari et al.2018) and 3) a hawaiitic basalt (Pasquarè et al.2008). To decouple the effect of granulometry and graphite content, we produced and analyzed different granulometric classes (ranging between <50 μm and 250μm) for each end-member. In a second stage, we selected three granulometric classes (<50 μm, 75-100 μm and 150-180 μm) for each end member and we added graphite producing different samples with graphite – silicate weight ratio between 0-5% (0%, 1%, 2%, 3%, 4% and 5%) in order to encompass the inferred graphite content in Mercury’s surface (Klima et al.2018). The results of our work confirm that graphite strongly decreases the contrast of the reflectance spectra of the silicate-graphite mixtures and, in most cases, has a negligible effect on the shift of the absorption bands. However the slopes of the reflectance spectra are greatly affected by the graphite content, which tends to decrease the slope of the spectra. Our systematic study will allow to gain a better understanding of the reflectance spectra of materials mixed with opaque phases in meteorites, space-weathered surfaces and rocky planetary bodies. In particular, this investigation is expected to have a strong impact on the interpretation of reflectance measurements of Mercury. Acknowledgments: Part of this research was supported by ASI-INAF Simbio-sys agreement. E.B. and C.C. are supported also by ASI-INAF 2018-16-HH.0 (Ol-BODIES) agreement.

How to cite: Bruschini, E., Carli, C., Capaccioni, F., Vincendon, M., Buellet, A.-C., Vetere, F., Secchiari, A., Ferrari, M., Perugini, D., and Montanini, A.: The effects of graphite and particles size on reflectance spectra of silicates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2704, https://doi.org/10.5194/egusphere-egu21-2704, 2021.

In situ composition measurements at Saturn and its moons (Cassini-Huygens^1,2) and at comet 67P/Churyumov-Gerasimenko (Rosetta^3,4) unveiled the complexity of the atmospheric chemical composition and high abundance of organic compounds in the environments of Solar System bodies. The deciphering of the measurements, obtained by current state-of-the-art instruments, to obtain the composition of complex gas mixtures that include polyatomic molecules and volatile organic compounds (VOCs) often requires having recourse to instrument response modeling supplemented by theoretical chemical models.

One of the limitations in currently flown mass spectrometers is their limited mass resolving power. High mass-resolving power offers the capability to identify unambiguously almost all complex organic compounds. Such technique offers identification of almost all complex organic compounds without application of complementary separation techniques, e.g. chromatography, spectroscopy or collision induced dissociation. A new generation of space mass spectrometers under development (MASPEX⁵, MULTUM⁶, CORALS⁷, CRATER⁷, among others), aims at reaching mass resolution of > 50 000. CORALS and CRATER are Orbitrap-based instruments using CosmOrbitrap elements.

In collaboration with J. Herovsky institute, the Laboratoire de Physique et de Chimie de l'Environnement et de l'Espace (LPC2E) has developed a new laboratory test-bench based on the Orbitrap™ technology OLYMPIA (Orbitrap anaLYseur MultiPle IonisAtion) to evaluate several space applications of an Orbitrap-based space instrument using different ionization techniques. OLYMPIA is a compact, transportable set-up and is intended to be used as a stand-alone device (currently with an EI ionization source), but later intended to be coupled to different sources of ions. The next step in the next few months is to couple it with the LLILBID set-up in Berlin⁸.

OLYMPIA is currently directly coupled with a first prototype of a compact electron impact ionization source. A single shot provides a useful signal duration of 200-250ms second before it decays to the noise level, and provide mass resolution for Kr ion isotopes of the order of 30 000 and on C₂H₄ on fragments of the order of 40 000. Kr is mostly being used to characterize the isotopic measurement capability of OLYMPIA and mixtures of C₂H₄, CO and N₂gases in different proportions.  In this presentation we concentrate on the capability to detect low ethylene lighter VOC concentration in different mixtures of CO and N₂. Sensitivity of the instrument is sufficient to detect traces of the carbon dioxide gas in mixture with molecular nitrogen abundant in less than 1% volume ratio.

1 Waite, J. H. et al. Space Sci. Rev. 114, 113–231 (2004)

2 Coates, A. J. et al. Geophys. Res. Lett. 34, (2007)

3 Balsiger, H. et al. Space Sci. Rev. 128, 745–801 (2007)

4 Le Roy, L. et al. A&A 583, (2015)

5 Brockwell, T. G. et al. in 2016 IEEE Aerospace Conference 1–17 (2016)

6 Shimma, S. et al. Anal. Chem. 82, 8456–8463 (2010)

7 Arevalo Jr, R. et al. Rapid Commun. Mass Spectrom. 32, 1875–1886 (2018)

8 Klenner, F. et al. Astrobiology 20, 179–189 (2019)

How to cite: Zymak, I., Sanderink, A., Gaubicher, B., Žabka, J., Lebreton, J.-P., and Briois, C.: OLYMPIA - a compact laboratory Orbitrap-based high-resolution mass spectrometer laboratory set-up: Performance studies for gas composition measurement in analogues of planetary environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8424, https://doi.org/10.5194/egusphere-egu21-8424, 2021.

Cosmic rays cause ionisation in all planetary atmospheres. As they collide with particles in the atmosphere, secondary charged particles are produced that lead to the formation of cluster ions. The incident cosmic ray flux and atmospheric density of the atmosphere in question determine a profile of ion production rate. From the top of the atmosphere to the planetary surface, this rate increases with atmospheric density to a point where the flux becomes attenuated such that the rate then decreases, resulting in a peak ion production rate at some height known as the Pfotzer-Regener maximum. When these ions interact with aerosols and cloud particles, a net charge results on those particles and this is known to affect their microphysical attributes and behaviour. For example, charging may enable the activation of droplets at lower saturation ratios and also enhance collision efficiency and droplet growth. This becomes important when clouds occur at a height where ionisation is sufficient to have a substantive charging effect on the cloud particles. This has very little direct effect on Earth as peak ion production occurs high above the clouds at 15-20 km; however, on Venus for example the Pfotzer-Regener maximum occurs at ~63 km, coinciding with the main sulphuric acid cloud deck. In situations such as this, the direct result of cloud charging due to cosmic ray induced ionisation may strongly influence cloud processes, their occurrence, and behaviour.

This work uses laboratory experiments to explore the effects of charging on cloud droplets. Individual droplets are levitated in a vertical acoustic standing wave and then monitored using a CCD camera with a high magnification objective lens to determine the droplet lifetime and evaporation rate. Experiments were conducted using both the droplets’ naturally occurring charge as well as some where the region around the drop was initially flooded with ions from an external corona source. The polarity and charge magnitude of the droplets was determined by applying a 10 kV/m electric field horizontally across the drop and observing its deflection towards one of the electrodes. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. This occurs when the droplet evaporates until its diameter becomes such that its fissility reaches the threshold at which the instability occurs. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. Therefore, where enhanced ionisation occurs in the presence of clouds the end result may be to reduce droplet stability.

How to cite: Airey, M., Harrison, G., Aplin, K., and Pfrang, C.: Effects of ionisation on cloud behaviour in planetary atmospheres, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13639, https://doi.org/10.5194/egusphere-egu21-13639, 2021.

In the Martian atmosphere, carbon dioxide (CO₂) clouds have been revealed by numerous instruments around Mars from the beginning of the XXI century. These observed clouds can be distinguished by two kinds involving different formation processes: those formed during the winter in polar regions located in the troposphere, and those formed during the Martian year at low- and mid-northern latitudes located in the mesosphere (Määattänen et al, 2013). Microphysical processes of the formation of these clouds are still not fully understood. However, modeling studies revealed processes necessary for their formation: the requirement of waves that perturb the atmosphere leading to a temperature below the condensation of CO₂ (transient planetary waves for tropospheric clouds (Kuroda et al., 20123), thermal tides (Gonzalez-Galindo et al., 2011) and gravity waves for mesospheric clouds (Spiga et al., 2012)). In the last decade, a state-of-the-art microphysical column (1D) model for CO₂ clouds in a Martian atmosphere was developed at Laboratoire Atmosphères, Observations Spatiales (LATMOS) (Listowski et al., 2013, 2014). We use our full microphysical model of CO₂ cloud formation to investigate the occurrence of these CO₂ clouds by coupling it with the Global Climate Model (GCM) of the Laboratoire de Météorologie Dynamique (LMD) (Forget et al., 1999). We recently activated the radiative impact of CO₂ clouds in the atmosphere. Last modeling results on Martian CO₂ clouds properties and their impacts on the atmosphere will be presented and be compared to observational data.

How to cite: Mathé, C., Määttänen, A., Audouard, J., Listowski, C., Millour, E., Forget, F., Spiga, A., Bardet, D., Teinturier, L., Falletti, L., Vals, M., González-Galindo, F., and Montmessin, F.: Global 3D modelling of Martian CO2 clouds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9457, https://doi.org/10.5194/egusphere-egu21-9457, 2021.

Mars’ polar vortices play a mjaor role in determining the global-scale transport of trace gases and the composition of the polar caps. Potential vorticity (PV) is a key quantity in determining their dynamical and transport properties. Mars' winter polar vortices are annular in PV, a direct contrast to Earth’s stratospheric polar vortices, whose PV values increase monotonically towards the poles. Given that a ring of high PV is known to be barotropically unstable, the persistence of this phenomenon in observations, simulations and reanalyses is somewhat surprising. Condensation of atmospheric carbon dioxide at the winter pole has been shown to be necessary to maintain the annulus in Martian Global Circulation Models (MGCM). Dust is also known to be a cause of internal and interannual variability in the polar vortices, but given the relatively few years of observations available, it is not yet fully understood. Here we present results of an attribution study of the driving mechanisms of the northern hemisphere Martian polar vortex. Using a reanalysis dataset and an idealized MGCM, we investigate the combined effects of dust, latent heat release, and topography on the polar vortex.

We show that the vertical PV structure of the polar vortex in the reanalysis is dependent on the observations assimilated, and that high atmospheric dust loading (such as that seen during a global dust storm) can disrupt the vortex and cause the destruction of PV in the low-mid altitudes. We also demonstrate that high dust loading can significantly reduce eddy activity within the core of the vortex over the course of a Martian winter. Latent heat release from carbon dioxide condensation is an important driver of variability within the polar vortex, but it is dust in the model that primarily drives the eddy activity throughout the Martian year.

How to cite: Ball, E., Mitchell, D., Seviour, W., Vallis, G., and Thomson, S.: Drivers of Mars' northern winter polar vortex, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7617, https://doi.org/10.5194/egusphere-egu21-7617, 2021.

How to cite: Holmes, J., Lewis, S., Patel, M., Chaffin, M., Cangi, E., Deighan, J., Schneider, N., Aoki, S., Fedorova, A., Kass, D., and Vandaele, A. C.: Enhanced water loss during the Mars Year 34 C storm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14926, https://doi.org/10.5194/egusphere-egu21-14926, 2021.

Carbon dioxide is the major constituent of the Martian atmosphere. Its seasonal cycle plays an important role in atmospheric dynamics and climate. Formation of the polar CO₂ frost deposits results in up to 30% of atmospheric pressure variations as well as in dramatic change in surface reflectance and emissivity. Another case of carbon dioxide condensation is formation of a CO₂ clouds that are still poorly studied, despite the fact that they have been observed by a number of instruments [1−6] on the orbit of Mars.

In this work, we will present first results of CO₂ clouds observations from a combination of thermal-infrared (1.7−17 µm) and near-infrared (0.7-1.6 µm) spectra measured by TIRVIM and NIR instruments onboard the ExoMars Trace Gas Orbiter (TGO) in solar occultation geometry. These instruments are part of the Atmospheric Chemistry Suite (ACS), a set of three spectrometers (NIR, MIR, and TIRVIM) that is conducting scientific measurements on the orbit of Mars since the spring of 2018 [7].

This work was funded by Russian Science Foundation, grant number 20-42-09035.

References

[1] Montmessin et al. (2006). Subvisible CO2 ice clouds detected in the mesosphere of Mars. Icarus, 183, 403–410. https://doi.org/10.1016/j.icarus.2006.03.015

[2] Montmessin et al. (2007). Hyperspectral imaging of convective CO2 ice clouds in the equatorial mesosphere of Mars. Journal of Geophysical Research, 112, E11S90. https://doi.org/10.1029/2007JE002944

[3] Määttänen et al. (2010). Mapping the mesospheric CO2 clouds on Mars: MEx/OMEGA and MEx/HRSC observations and challenges for atmospheric models. Icarus, 209, 452–469. https://doi.org/10.1016/j.icarus.2010.05.017

[4] McConnochie et al. (2010). THEMIS-VIS observations of clouds in the Martian mesosphere: Altitudes, wind speeds, and decameter-scale morphology. Icarus, 210, 545–565. https://doi.org/10.1016/j.icarus.2010.07.021

[5] Vincendon et al. (2011). New near-IR observations of mesospheric CO2 and H2O clouds on Mars. Journal of Geophysical Research, 116, E00J02. https://doi.org/10.1029/2011JE003827

[6] Jiang et al., (2019). Detection of Mesospheric CO 2 Ice Clouds on Mars in Southern Summer. Geophysical Research Letters, 46(14), 7962–7971. https://doi.org/10.1029/2019GL082029

[7] Korablev et al., (2018). The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev. 214, 7. doi:10.1007/s11214-017-0437-6

How to cite: Luginin, M., Ignatiev, N., Fedorova, A., Trokhimovskiy, A., Grigoriev, A., Shakun, A., Montmessin, F., and Korablev, O.: Observations of CO2 clouds on Mars from TIRVIM and NIR solar occultation measurements onboard TGO, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12721, https://doi.org/10.5194/egusphere-egu21-12721, 2021.

   Mars may have obtained a proto-atmosphere enriched in H₂, CH₄, and CO during accretion. Such a reduced proto-atmosphere would have been largely lost by hydrodynamic escape, but its flux is highly uncertain. To estimate the evolution of the proto-atmosphere of Mars correctly, an exact escape modeling including exact radiative balance and chemical processes is required partly because those reduced species and their photochemical products may act as an effective coolant that suppresses the escape of atmosphere. Here we develop a one-dimensional hydrodynamic escape model that includes radiative processes and photochemical processes for a multi-component atmosphere and apply to the reduced proto-atmosphere on Mars.

   Under the enhanced XUV flux suggested for young Sun, the escape flux decreases by more than one order of magnitude with increasing the mixing fraction of CH₄ and CO  from zero to > 10 % mainly because of the energy loss by radiative cooling by these infrared active chemical molecules. Concurrently, the mass fractionation between H₂ and other heavier species becomes to be enhanced. Given that the proto-Mars initially obtained > 10 bar of H₂ and carbon species equivalent to 1 bar of CO₂ was then left behind after the end of the hydrodynamic escape of H₂, the total amount of carbon species lost by hydrodynamic escape is estimated to be equivalent to 20 bar of CO₂ or more. Such a severe loss of carbon species may explain the paucity of CO₂ on Mars compared to Earth and Venus. If the proto-Mars obtained > 100 bar of H₂, the timescale for H₂ escape exceeds ~100 Myr. This implies that an atmosphere with reduced chemical compositions allowing the production of organic matter deposits may have been kept on early Mars traceable by geologic records.

How to cite: Yoshida, T. and Kuramoto, K.: Sluggish hydrodynamic escape of early Martian atmosphere with reduced chemical compositions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10804, https://doi.org/10.5194/egusphere-egu21-10804, 2021.

For fifteen years, a Global Climate Model (GCM) has been developed for the Venus atmosphere at Institut Pierre-Simon Laplace (IPSL), in collaboration between LMD and LATMOS, from the surface up to 150 km altitude. Its recent extension up to the exobase (roughly 250 km) within the framework of the VCD project now allows us to simulate the Venusian upper atmosphere and the key atmospheric parameters of the aerobraking phases. The aim of this presentation is to study the evolution of the density of the Venusian upper atmosphere as a function of different parameters such as solar irradiance, latitude, local time and zenith solar angle (SZA), for regions from 130 to 180 km of altitude. We will present here several comparisons of the upper atmosphere of Venus between our model results and a selection of aerobraking data from different missions such as Venus Express, Pioneer Venus and Magellan.

How to cite: Martinez, A., Lebonnois, S., Chaufray, J.-Y., Millour, E., and Pierron, T.: Comparison between IPSL Venus Global Climate Model results and aerobraking data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5025, https://doi.org/10.5194/egusphere-egu21-5025, 2021.

General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/swith rates of 0.2–0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.

How to cite: Yamamoto, M., Hirose, T., Ikeda, K., and Takahashi, M.: Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3657, https://doi.org/10.5194/egusphere-egu21-3657, 2021.

The Io Volcano Observer (IVO) is a proposed NASA Discovery-class mission (currently in Phase A), that would launch in early 2029, arrive at  Jupiter in the early 2033, and perform ten flybys of Io while in Jupiter's orbit. IVO's mission motto is to 'follow the heat', shedding light onto tidal heating as a fundamental planetary process. Specifically, IVO will determine (i) how and where heat is generated in Io's interior, (ii) how heat is transported to the surface, and (iii) how Io has evolved with time. The answers to these questions will fill fundamental gaps in the current understanding of the evolution and habitability of many worlds across our Solar System and beyond where tidal heating plays a key role, and will give us insight into how early Earth, Moon, and Mars may have worked.

One of the five key science questions IVO will be addressing is determining Io's mass loss via atmospheric escape. Understanding Io's mass loss today will offer information on how the chemistry of Io has been altered from its initial state and would provide useful clues on how atmospheres on other bodies have evolved over time. IVO plans on measuring Io's mass loss in situ with the Ion and Neutral Mass Spectrometer (INMS), a successor to the instrument currently being built for the JUpiter Icy moons Explorer (JUICE). INMS will measure neutrals and ions in the mass range 1 – 300 u, with a mass resolution (M/ΔM) of 500, a dynamic range of > 10⁵, a detection threshold of 100 cm^–3 for an integration time of 5 s, and a cadence of 0.5 – 300 s per spectrum.

In preparation for IVO, we model atmospheric density profiles of species known and expected to be present on Io's surface from both measurements and previous modelling efforts. Based on the IVO mission design, we present three different measurement scenarios for INMS we expect to encounter at Io based on the planned flybys: (i) a purely sublimated atmosphere, (ii) the 'hot' atmosphere generated by lava fields, and (iii) the plume gases resulting from volcanic activity. We calculate the expected mass spectra to be recorded by INMS during these flybys for these atmospheric scenarios.

How to cite: Wurz, P., Vorburger, A., McEwen, A., Mandt, K., Davies, A., Hörst, S., and Thomas, N.: Modelling of Io’s Atmosphere for the IVO Mission, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-778, https://doi.org/10.5194/egusphere-egu21-778, 2021.

Exoplanets provide excellent laboratories to explore novel atmospheric regimes; using observations coupled with microphysical models we can probe our understanding of the formation and evolution of planets beyond those in the Solar System. However, clouds remain a key challenge in observation of exoplanet atmospheres, both altering the local atmospheric composition and obscuring deeper atmospheric layers. Currently, most observed exoplanet atmospheres are tidally locked gas-giants in close orbit around their host star. These hot and ultra-hot Jupiters have day-side temperatures in excess of 2500 K, and still above 400 K on the night-side, thus they form solid clouds made of minerals, metal oxides and metals. These clouds may form snowflake like structures, either through condensation or by constructive collisions (coagulation).

We explore the effects of non-compact, non-spherical cloud particles in gas-giant exoplanet atmospheres by expanding our kinetic non-equilibrium cloud formation model, to include parameterised porous cloud particles as well as cloud particle growth and fragmentation through collisions. We apply this model to prescribed 1D temperature - pressure Drift-Phoenix atmospheric profiles, using Mie theory and effective medium theory to study cloud optical depths, representing the effects of the non-spherical cloud particles through a statistical distribution of hollow spheres.

Finally, we apply our cloud formation model to a sample of gas-giants as well as ultra-hot Jupiters, using 1D profiles extracted from the 3D SPARC/MITgcm general circulation model. In particular, we take the example cases of gas-giant WASP-43b and the ultra-hot Jupiter HAT-P-7b, where we find dramatic differences in the day-/night-side distribution of clouds between these types of exoplanets due to the intensity of stellar irradiation for HAT-P-7b. Further an asymmetry in cloud coverage at the terminators of ultra-hot Jupiters is observable in the optical depth of the clouds, which affects the observable atmospheric column and thus has implication for detection of key gas phase species. Clouds also enhance the gas phase C/O which is often used as an indicator of formation history. With next-generation instruments such as the James Webb Space Telescope (JWST) such details will begin to be examined, but we find that a detailed understanding of cloud formation processes will be required to interpret observations.

How to cite: Samra, D., Helling, C., Min, M., and Birnstiel, T.: Modelling Mineral Snowflakes in the Atmospheres of Gas-Giant Exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10235, https://doi.org/10.5194/egusphere-egu21-10235, 2021.

How to cite: Lewis, N. and Read, P.: Planetary and atmospheric properties leading to strong super-rotation in terrestrial atmospheres studied with a semi-grey GCM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4855, https://doi.org/10.5194/egusphere-egu21-4855, 2021.

Rocky extrasolar planets orbiting M dwarfs are prime targets in the search for habitable surface conditions and biosignatures with near-future telescopes like the James Webb Space Telescope (JWST) and the Extremely Large Telescope (ELT). Even for the closest known targets the capabilities to characterize Earth-like or CO₂-dominated atmospheres with JWST or ELT might still be limited to a few molecules such as CO₂ or CH₄. Hence it would be difficult to draw conclusions on the surface conditions and potential habitability of these planets. In clear H₂-He atmospheres the molecular features in transmission spectra could be much larger and hence potential biosignatures might be detectable.

In this study, we investigate the detectability of the potential biosignatures NH₃, PH₃, CH₃Cl, and N₂O, assuming different H₂-He atmospheres for the habitable zone super-Earth LHS 1140 b. Recent observations of the atmosphere of LHS 1140 b suggest that the planet might hold a clear H₂-dominated atmosphere and might show an absorption feature around 1.4 µm due to H₂O or CH₄ absorption. Here we use the coupled convective-climate-photochemistry model 1D-TERRA to simulate H₂ atmospheres of LHS 1140 b with different amounts of CH₄ and assuming that the planet has an ocean and a biosphere.

The destruction of the potential biosignatures NH₃, PH₃, CH₃Cl, and N₂O shows a weak dependence on the concentrations of CH₄. For weak abundances of CH₄ only 5 to 10 transits are required to detect these molecules with JWST or ELT. However, for CH₄ surface mixing ratios of a few percent only NH₃ and N₂O might be detectable with less than 10 transits. A scenario with large abundances of CH₄ is consistent with the spectral feature at 1.4 µm and such an atmosphere might allow habitable surface temperatures. If this spectral feature at 1.4 µm originates from H₂O absorption, the planet is likely not habitable at the surface.

How to cite: Wunderlich, F., Scheucher, M., Grenfell, J. L., Schreier, F., Sousa-Silva, C., Godolt, M., and Rauer, H.: Detectability of biosignatures on LHS 1140 b, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15410, https://doi.org/10.5194/egusphere-egu21-15410, 2021.

A first sounding rocket campaign dedicated to investigate the creation mechanism of Polar Mesosphere Winter Echoes (PMWE) was conducted in April 2018 from the north Norwegian Andøya Space Center (69°N, 16°E). Two instrumented sounding rockets were launched on 13th and 18th of April under PMWE and no-PMWE conditions, respectively.

In this paper we give a brief summary of our current knowledge of PMWE and an overview of the PMWE sounding rocket mission. We describe and discuss some results of combined in situ and ground-based measurements which allow to check the existing PMWE theories.

Our measurements clearly show that the coherent structures in refractive index variations (forming PMWE) are accompanied by neutral air turbulence, which is reflected in small-scale structures (down to some meters) of neutral and electron density. We show that the behavior of the structures under investigation together with the atmospheric background is consistent with the interpretation, that PMWE were created by turbulence. Rocket measurements ultimately show that polar winter mesosphere is abounded with meteor smoke particles (MSP) and intermittent turbulent layers. Furthermore, it becomes clear that charged Meteor Smoke Particles (MSP) and background electron density can only enhance SNR, while turbulence is a prerequisite for their formation.

How to cite: Strelnikov, B. and the sounding rocket project PMWE team: PMWE creation mechanism inferred from sounding rocket measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4186, https://doi.org/10.5194/egusphere-egu21-4186, 2021.

The ablation of cosmic dust particles is a source of metallic vapours in planetary upper atmospheres. Recently, ground-based lidars have made the first observations of a layer of Ni atoms peaking around 86 km in the terrestrial atmosphere (in contrast, the layers of Na and Fe have been observed for several decades).  In order to understand these Ni layer observations, we have developed a new version of the Leeds Chemical Ablation Model (CAMBOD) to include a Ni-Fe-S metallic phase in addition to the bulk silicate phase. The validity of the new model was tested using our laboratory Meteoric Ablation Simulator, where micron-size meteoritic particles were flash heated to temperatures as high as 2700 K to simulate their atmospheric entry, and the ablating Ni atoms monitored by fast time-resolved laser induced fluorescence.

The first global atmospheric model of Ni (WACCM-Ni) was then developed with three components: the Whole Atmosphere Community Climate Model (WACCM6); a meteoric input function derived by coupling an astronomical model of dust sources in the solar system with CABMOD; and a comprehensive set of neutral, ion-molecule and photochemical reactions pertinent to the chemistry of Ni in the upper atmosphere. The kinetics of these reactions were mostly measured in our laboratory, or else modelled theoretically using ab initio quantum calculations combined with statistical rate theory. WACCM-Ni simulates satisfactorily the observed neutral Ni layer peak height and width, as well as Ni⁺ ion measurements from rocket-borne mass spectrometry. The Ni layer is predicted to have a similar seasonal and latitudinal variation as the Fe layer, and its unusually broad bottom-side compared with Fe is caused by the relatively fast NiO + CO → Ni + CO₂ reaction. The quantum yield for photon emission from the reaction between Ni and O₃, which has been observed in the nightglow from space-based spectrometers, is estimated to be between 6 and 40%.

How to cite: Plane, J., Daly, S., Feng, W., Mangan, T., Gerding, M., Carrillo Sanchez, J. D., and Bones, D.: The Meteoric Ni Layer in the Upper Atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12636, https://doi.org/10.5194/egusphere-egu21-12636, 2021.

For two decades meteor radars have been routinely used to monitor atmospheric temperatures around the 90 km altitude. A common method, based on a temperature-gradient model, is to use the height dependence of meteor decay time to obtain a height-averaged temperature in the peak meteor region. Traditionally this is done by  fitting a linear regression model in the scattered plot of  log₁₀(1/tau) and height, where ’tau’ is the half-amplitude decay time of the received signal. However, this method was found to be consistently biasing the slope estimate. The consequence of such bias is that it produces a  systematic offset in the estimated temperature, and thus requiring calibration with other colocated measurements. The main reason for such a biasing effect is thought to be due to the failure of the classical regression model to take into account the measurement error in decay time or the observed height. This is further complicated by the presence of various geophysical effects in the data, as well as observational limitation in the measuring instruments. We demonstrate an alternative regression method that incorporates various error terms in the statistical model. An initial estimate of the slope parameter is obtained by assuming symmetric error variances in normalised height and log₁₀(1/tau). This solution is found to be a good prior solution for the core of this bivariate distribution. However, depending on the data selection process the error variances may not be exactly equal. A first-order correction is then carried out to address the biasing effect due to asymmetric error variances. This allows to construct an analytic solution for the bias-corrected slope coefficient for this data. With this solution, meteor radar temperatures can be obtained independently without using any external calibration procedure. When compared with colocated lidar measurements, the temperature estimated using this method is found to be accurate within 7% or better and without any systematic offset.

How to cite: Sarkar, E., Ulich, T., Virtanen, I., Lester, M., Kaifler, B., and Kozlovsky, A.: Solving the long-standing problem of estimating the atmospheric temperature at 90 km altitude with meteor radar, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14760, https://doi.org/10.5194/egusphere-egu21-14760, 2021.

BRAMS (Belgian RAdio Meteor Stations) is a Belgian radio network using forward scatter observations to detect and characterize meteoroids. A dedicated transmitter located in south of Belgium emits a CW signal with no modulation at a frequency of 49.97 MHz and with a power of 130 W. The network comprises currently 35 similar receiving stations located in Belgium and neighboring countries. They use Yagi antennas with a wide sensitivity pattern which therefore provide no information about the directivity of the meteor echoes. One of these stations is however a radio interferometer using the classical Jones configuration and is able to retrieve the direction of the meteor echoes.

We discuss here a general method to retrieve meteoroid trajectories based solely on time delays measured between meteor echoes recorded at multiple receiving stations. It is based on solving at least 6 non-linear equations to solve for the position of one specular reflection point (3 unknowns) and the 3 components of the speed. This method has also been described recently in Mazur et al (2020) and applied to CMOR data. However, specificities of the CMOR configuration has allowed simplifications that cannot be made with the BRAMS network. In order to maximize the number of meteoroid trajectories with at least 6 stations detecting meteor echoes, a number of additional stations geographically close to each other have been installed in the Limburg province in 2020. Another method to retrieve meteoroid trajectories using data from the radio interferometer and from 3 other stations is also presented.

We show preliminary results from both methods using also complementary data from the optical CAMS Benelux network.  The CAMS trajectories are used to select specific meteor echoes in the BRAMS data. The time delays between them are computed and used to solve the set of non-linear equations to retrieve the meteoroid trajectory and speed, which are then compared to the CAMS values. This allows us to assess the accuracy of both methods.

Finally we simulate the impact of using additional information, not currently available but that might become in a near future. This includes data from a monostatic system (a radar nearby our BRAMS transmitter is currently built), from a second radio interferometer (to be located in Limburg and/or near the transmitter), or the total range traveled by the radio wave if a coded CW transmitter such as in Vierinen et al (2016) is used.

How to cite: Lamy, H.: Meteoroid trajectories from BRAMS data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14249, https://doi.org/10.5194/egusphere-egu21-14249, 2021.

International cooperation has definitely been shaping the development of the Corpus Juris Spatialis and relative principles under the aegis of the United Nations (see A/Res/1962/XVIII). To this extent, the concept of space as global commons represents the core debate of Space Agencies (ESA), whilst manned and unmanned exploration of the universe are flying to next generation. On the other hand, all space activities will be reasonably linked to both anthropic and natural risks: other effective provisional advancements in international space law are so much needed to addressing space debris and planetary defense as common global challenges

First of all, the space debris issue is susceptible to fostering the aferomentioned level of innovation in space law by these multilateral efforts. All “composite material components” accumulating in considerable amount in Low-Earth Orbit (LEO/collinear Lagrangian points) may possibly lead the way to a comprehensive review of the terms laid down in the Outer Space Treaty (ex plurimis, article IX). Morevover, the further existence of international customary law, which is notably ascertained “as evidence of a general practice accepted as law” (art. 38, let. b, ICJ Statute), might also create hermeneutical tools to tackling such critical task. In addition, a long-term solution may hopefully give birth to the establishment of an international agreement on space debris clearing, providing for adequate international binding norms and structural organization of international guidelines (IADC/UNOOSA) 

Secondly, planetary defense measures vis-à-vis the so called “Cosmic Hazard” shall be carried out by emphasizing the application of international space law and regulations thereto. In particular, the legal use of explosive devices (NED) may be found as slightly critical in light of the applicable international norms and regulations. Moreover, cosmic hazard issues also engage with a very complex level of decision making, to be carried out by a specific vote of the United Nation Security Council (UNSC) in application of the procedure laid down in article 27 of the UN Charter. On the other side, this particular dilemma may call upon States to undertake responses against natural space threats by preventing potential liability of the States (see article VII OST and International Liability Convention for Damages caused by Space Objects)

Eiusmodo, the liability conventional framework shall either have some comprehensive interpretation of the principle of “vis major (quae humana infirmitas resistere non potest)”. In compliance with article II, it must be noticed that failing attempts by Parties- whenever space threats may be encountered in different circumstances  - connects directly with the regime of absolute responsibility for eventual damages occurred to third Parties.

To be concluded, both space debris and planetary defense stand together as resilient pillars of international cooperation in space affairs: the accountable exploration of outer space shall previously take also into account of such perspectives for the exclusive benefit of Mankind  

How to cite: De Blasi, D.: From space debris to planetary defense: a provisional ground for resilient international cooperation in outer space activities  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-492, https://doi.org/10.5194/egusphere-egu21-492, 2021.

In the frame work of HERA mission, the gravimeter for small solar system objects (GRASS) has been developed to measure the local acceleration vector on the surface of the moonlet of the binary asteroid, Dimorphos. GRASS will be onboard Juventas CubeSat which is one of the two daughtercraft of ESA’s Hera spacecraft. Launched in 2024 it will arrive in the binary system in 2026. Following the soft-landing of the Juventas CubeSat, GRASS will record the temporal variation of the surface gravity vector.

The average gravitational force expected on the Dimorphos surface is around 5 x 10^-5 m s^-2 (or 5 mGal). Apart from the self-gravitation of the body, centrifugal forces and the acceleration due to the main body of the system contribute to the surface acceleration. The temporal variations of local gravity vector at the landing site will be used to constrain the geological substructure (mass anomalies, local depth and lateral variations of regolith) as well as the surface geophysical environment (tides, dynamic sloped and centrifugal forces).

We will present the GRASS science objectives in the Hera mission the operational concept that is foreseen to reach these objectives, its current status of development including first test results and the by simulation estimated performances of the instrument.

How to cite: Karatekin, Ö., Ritter, B., Carrasco, J., Noeker, M., Umit, E., Vanransbeeck, E., Alaves, H., Tasev, E., Goli, M., Van waal, S., and Goldberg, H.: Surface gravimetry on Dimorphos  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15901, https://doi.org/10.5194/egusphere-egu21-15901, 2021.

The Asteroid Impact and Deflection Assessment (AIDA) is an international collaboration supported by ESA and NASA to assess the feasibility of the kinetic impactor technique to deflect an asteroid, combining data obtained from NASA’s DART and ESA’s Hera missions. Together the missions represent the first humankind’s investigations of a planetary defense technique. In 2022, DART will impact Dimorphos, the secondary of the binary near-Earth asteroid (65803) Didymos.  After 4 years, Hera will follow-up with a detailed post-impact survey of Didymos, to fully characterize and validate this planetary defense technique. In addition, Hera will deploy two CubeSats around Didymos once the Early Characterization Phase has completed, to augment the observations of the mother spacecraft. Juventas, the first Cubesat, will complete a low-frequency radar survey of the secondary, to unveil its interior. Milani, the second Cubesat, will perform a global mapping of Didymos and Dimorphos, with a focus on their compositional difference and their surface properties. One of the main objectives of Hera is to determine the binary system’s mass, gravity field, and dynamical state using radio tracking data in combination with imaging data. The gravity science experiment includes classical ground-based radiometric measurements between Hera and ground stations on Earth by means of a standard two-way X-band link, onboard images of Didymos, and spacecraft-to-spacecraft inter-satellite (ISL) radiometric tracking between Hera and the Cubesats. The satellite-to-satellite link is a crucial add-on to the gravity estimation of low-gravity bodies by exploiting the Cubesats’ proximity to the binary, as the range-rate measurements carried out by the inter-satellite link contain information on the dynamics of the system, i.e., masses and gravity field of Didymos primary and secondary.

We will describe the updated mission scenario for the Hera radio science experiment to be jointly carried out by the three mission elements, i.e., Hera, Juventas and Milani. To conclude, our updated analysis and latest results, as well as the achievable accuracy for the estimation of the mass and gravity field of Didymos and Dimorphos, are presented.

How to cite: Tortora, P., Zannoni, M., Gramigna, E., Lasagni Manghi, R., Le Maistre, S., Park, R. S., Tommei, G., Karatekin, O., Goldberg, H., Martino, P., Concari, P., Kueppers, M., Michel, P., and Carnelli, I.: Didymos Gravity Science Investigations through Ground-based and Inter-Satellite Links Doppler Tracking, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14898, https://doi.org/10.5194/egusphere-egu21-14898, 2021.

The Dawn mission at Asteroid 4 Vesta revealed two sets of enormous linear structures. Both sets are troughs—linear, negative-relief landforms—with one spanning around at least two-thirds of the equator and the other set incompletely preserved in the northern hemisphere. A previous study evaluated the cross-sectional geometries of the troughs and interpreted them as analogous to grabens, which are landforms caused by normal faults. However, for the troughs to be large-scale opening-mode fractures, i.e., joints, was heretofore not considered. To distinguish between normal faulting and jointing, we investigated the map patterns, cross-sectional geometries, and variations of relief and width along the length of these troughs. Relief and width are meaningful measurands that causally relate to the vertical displacement of faults or aperture of joints, respectively. Their distributions along the trough length should thus reveal differences in fracturing behavior. In addition, we derived strength-depth profiles to characterize the rheologic structure of Vesta’s lithosphere and determine the predicted fracturing behavior in its brittle regime.

We mapped all large-scale troughs on Vesta, including four equatorial and two northern troughs, and no map patterns diagnostic for faulting were identified. The troughs are bounded by scalloped rims and mainly show V- and bowl shapes in cross-section. The variation of reliefs of the two-opposing trough-bounding scarps reveals that the relief maxima for each of the investigated troughs are located off-center, and at different locations along the trough they bound. In contrast, we found that both the individual and cumulative variations in trough width have their maxima near the center of the trough. These map patterns and geomorphologic characteristics are largely inconsistent with the mechanics of graben formation but instead point to an origin by opening-mode fracturing. Moreover, our calculations of lithospheric strength evolution that enable assessments of fracturing behavior reveal that Vesta’s lithosphere has been dominated by a thick brittle portion throughout its history. Solutions to the Coulomb criterion considering a range of strengths properties of intact to fractured basaltic materials are in support of jointing as the major fracturing mode in at least the upper ~14 km of Vesta’s lithosphere.

How to cite: Cheng, H. C. J. and Klimczak, C.: The large-scale troughs on Asteroid 4 Vesta are opening-mode fractures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-79, https://doi.org/10.5194/egusphere-egu21-79, 2021.

Comets show a general diversity in their parent volatile composition, but in most cases H₂O is observed to be the dominant volatile in terms of abundance. This is followed by CO and CO₂, and trace amounts of other species such as CH₄, CH₃OH, O₂, and NH₃ are also present. However, the observed ratio of n_x/H₂O varies considerably from one comet to another (n_x represents any parent species other than water).

We aim to study how the chemistry and dynamics of the cometary coma changes for varying abundances of the major parent volatiles. We have constructed a fluid model, using the principles of conservation of mass, momentum and energy, for our study. Parent volatiles sublimating from the nucleus undergo photolytic reactions due to the solar UV radiation field, resulting in the formation of secondary neutral and ionic species and photoelectrons. Active chemistry occurs in the coma, and some of the chemical reactions taking place are ion-neutral rearrangement, charge exchange, dissociative recombination, electron impact dissociation and radiative de-excitation. The energy that is released due to these chemical reactions is non-uniformly distributed amongst all the species, resulting in different temperatures. Hence,  for a complete description of the coma, we have used a multifluid model whereby the neutrals, ions and electrons are considered as three separate fluids. Apart from chemical reactions, we have also considered the exchange of energy between the three fluids due to elastic and inelastic collisions.

We consider different initial compositions of the comet, and then use our model to generate the temperature and velocity profiles of the coma, for varying cometocentric distances. We also obtain the number density profiles of the different ionic and neutral species that are created in the coma. We see that changes in the initial parent volatile abundance will modify the temperature profile, and there are significant changes in the ionic abundances. Hence, the parent volatile composition of the comet drives the physico-chemical attributes of the coma.

How to cite: Ahmed, S. and Acharyya, K.: Multifluid modelling of cometary coma for diverse range of parent volatile compositions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14559, https://doi.org/10.5194/egusphere-egu21-14559, 2021.

Line-of-sight integration of emissions from planetary and cometary atmospheres is the Abel transform of the emission rate, under the spherical symmetry assumption. Indefinite integrals constructed from the Abel transform integral are useful for implementing remote sensing data analysis methods, such as the numerical inverse Abel transform giving the volume emission rate compatible with the observation. We obtain analytical expressions based on a suitable, non-alternating, series development to compute those indefinite integrals. We establish expressions allowing absolute accuracy control of the convergence of these series depending on the number of terms involved. We compare the analytical method with numerical computation techniques, which are found to be sufficiently accurate as well. Inverse Abel transform fitting is then tested in order to establish that the expected emission rate profiles can be retrieved from the observation of both planetary and cometary atmospheres. We show that the method is robust, especially when Tikhonov regularization is included, although it must be carefully tuned when the observation varies across many orders of magnitude. A first application is conducted over observation of comet 46P/Wirtanen, showing some variability possibly attributable to an evolution of the contamination by dust and icy grains. A second application is considered to deduce the 557.7 nm volume emission rate profile of the metastable oxygen atom in the upper atmosphere of planet Mars.

How to cite: Hubert, B., Munhoven, G., Moulane, Y., Hutsemekers, D., Manfroid, J., Opitom, C., Jehin, E., Aoki, S., Soret, L., Gkouvelis, L., and Gérard, J.-C.: Abel transform of exponential functions for planetary and cometary atmospheres with application to observation of 46P/Wirtanen and to the OI 557.7 nm emission at Mars., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9244, https://doi.org/10.5194/egusphere-egu21-9244, 2021.

While the volatile species in comet 67P/Churyumov-Gerasimenko’s coma have been analyzed in great spatial and temporal detail, e.g., Rubin et al. (2019) or Läuter et al. (2020), little is so far known about the less volatile, heavier species. There is growing evidence, however, that less volatile species, such as salts, may play a key role in explaining some of the puzzling properties of comets, as for instance shown by Altwegg et al. (2020). These authors also have demonstrated the unique capability of ROSINA/DFMS (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/ Double Focusing Mass Spectrometer; Balsiger et al. (2007)) to detect exactly such little volatile species in-situ, namely during a dust event on 5 September 2016 (when a dust grain entered the instrument and sublimated inside).

Complementary information on 67P’s dusty coma can be obtained from data collected during time periods of high dust activity. A clear advantage of such data is they also allow for a quantitative interpretation thanks to the much more stable measurement conditions. Moreover, a comparison to data collected during a time period of little dust activity (e.g., to the days around end of May 2015 as in Rubin et al. 2019) also allows to link species to dust.

End of July / beginning of August 2015, the comet was approaching its perihelion and ejecting a lot of dust, as seen by the OSIRIS camera (Vincent et al. 2016). The data from this period are therefore a promising starting point for the search of heavier species (m > 100 Da). Altwegg et al. (2019), for instance, reported on the tentative identifications of the simplest polyaromatic hydrocarbon species naphthalene as well as of benzoic acid, the simplest aromatic carboxylic acid. To confirm these identifications and to achieve a more complete inventory of heavier and chemically more complex species, we are now analyzing these data sets strategically. In our contribution we will share what we have learned from pushing the exploration of 67P’s dusty coma.

Altwegg et al., 2020, Nat. Astron., 4, 533-540.
Altwegg et al., 2019, Annu. Rev. Astron. Astrophys., 57, 113-55.
Balsiger H. et al., 2007, Space Sci. Rev., 128, 745-801.
Läuter et al., 2020, MNRAS, 498, 3, 3995-4004.
Rubin et al., 2019, MNRAS, 489, 594-607. Vincent et al., 2016, MNRAS, 462 (Suppl_1), 184-194.

How to cite: Hänni, N., Altwegg, K., Müller, D., Pestoni, B., Rubin, M., and Wampfler, S.: Analyzing 67P’s dusty coma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1719, https://doi.org/10.5194/egusphere-egu21-1719, 2021.

A full-mission analysis of Cl-bearing species in the coma of comet 67P/Churyumov-Gerasimenko has been conducted using data from the Rosetta ROSINA/DFMS mass spectrometer. This contribution will focus on the challenges encountered to relate DFMS data on Cl-bearing species to the neutral abundances at the comet.

DFMS was operated in neutral mode, in which electron impact ionizes a fraction of the incoming neutral gas in the ion source. Only ions in a narrow range around a certain commanded mass-over-charge ratio (m/z) pass through the mass analyser at a time and impact on a micro-channel plate (MCP), creating an electron avalanche that is recorded by a Linear Electron Detector Array chip with two rows of 512 pixels each (LEDA A and LEDA B). Data are obtained as Analog-to-Digital Converter (ADC) counts as a function of LEDA pixel number. The instrument scans over a sequence of m/z values.

A well-defined approach exists to convert ADC counts as a function of pixel number to the number of ions that were detected on the MCP. However, to relate the number of ions detected this way to the abundance of neutrals in the coma gas, the sensitivity for each neutral needs to be known. The sensitivity for a certain neutral takes into account the total ionization cross section for the neutral and product ion fraction, instrument transmission and secondary electron yield for each product ion. Sensitivities can be determined experimentally by introducing the neutrals in the DFMS instrument copy in the laboratory, but such data are not available for Cl-bearing species and an alternative approach needs to be used. Fortunately, the use of ratios cancels out some of the factors that play a role in the sensitivity. As an example, for the ³⁷Cl/³⁵Cl ratio, total ionization cross sections and product ion fractions can be considered identical. In the case of ³⁷Cl/³⁵Cl, taking into account the sensitivity results in a correction of more than 15%, mainly due to the secondary electron yield.

The ³⁷Cl/³⁵Cl ratio does not appear to change appreciably throughout the mission and is compared with known values from other solar system objects. The Cl/HCl ratio obtained with DFMS indicates that there must be at least one additional chlorine-bearing species on the comet next to HCl, CH₃Cl and NH₄Cl, the identity of which is unknown at this time.

How to cite: Dhooghe, F., De Keyser, J., Hänni, N., Altwegg, K., Cessateur, G., Jehin, E., Rubin, M., and Wurz, P.: Chlorine-bearing species and the 37Cl/35Cl isotope ratio in the coma of comet 67P/Churyumov-Gerasimenko, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10601, https://doi.org/10.5194/egusphere-egu21-10601, 2021.

Following its arrival at 67P/Churyumov-Gerasimenko in August 2014, the Rosetta spacecraft successfully navigated in proximity of the comet for two years, using a combination of radiometric measurements and optical images collected by the onboard navigation cameras.

The reconstructed spacecraft and comet trajectories were obtained combining several long-arc and short-arc orbit determination solutions generated by ESOC Flight Dynamics during the Rosetta operations. Several discontinuities are present within these trajectories, due to the lack of a dynamical model for the representation of the comet Non-Gravitational Accelerations (NGA).

The work presented in this study represents an effort to produce an accurate and continuous ephemeris reconstruction for comet 67P/Churyumov-Gerasimenko for the period between July 2014 and October 2016, through a complete reanalysis of the Range and ΔDOR measurements collected by Rosetta during its proximity phase with the comet.

Using as input the reconstructed relative orbit of Rosetta, the radiometric observables were mapped to the comet nucleus and used to estimate the comet state and some key physical and observational parameters within a Square Root Information batch filter implemented in MONTE, most notably the NGA acting on the comet nucleus due to surface outgassing.

Several orbit determination solutions were generated by varying the model used to represent the NGA. More specifically, empirical and stochastic models were compared by evaluating the reduced χ² statistics of the measurement residuals to identify the most suitable trajectory estimations for each of the proposed models. From this narrow list of solutions, a preliminary selection for the final ephemeris reconstruction is proposed, based on its adherence to the original ESOC trajectory and on the consistency of the formal state uncertainties with the estimated solutions.

It will be shown that the selected ephemeris solution, using a piecewise linear stochastic NGA model with intervals between 3 and 4 weeks, produces a continuous ephemeris reconstruction for 67P/Churyumov-Gerasimenko with maximum formal uncertainties around perihelion of σ_pos ≅ [20 km, 30 km, 200 km] in the Radial-Tangential-Normal reference frame. The advantage of using simple stochastic models, with limited a-priori assumptions on the involved physical processes, is that they allow to produce an unbiased estimation of the NGA variations around perihelion, which represent a valuable input for further investigations involving detailed physical models of the cometary activity.

How to cite: Lasagni Manghi, R., Zannoni, M., Tortora, P., Küppers, M., O'Rourke, L., Martin, P., Mottola, S., Budnik, F., Mackenzie, R., Godard, B., Jorda, L., Groussin, O., and Thomas, N.: Accurate ephemeris reconstruction for comet 67P/Churyumov-Gerasimenko from Rosetta data analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14765, https://doi.org/10.5194/egusphere-egu21-14765, 2021.

The varying geometry of Cassini star occultations by Saturn’s rings constrains both the size and shape of structures that block starlight. Statistics of UVIS star occultations measure structures as small as meters, on times scales of minutes to decades. We calculate the excess variance, skewness and kurtosis including the effects of irregular particle shadows, along with a granola bar model of gaps, ghosts and clumps. The widths W and separation S of rectangular clumps play an analogous role to the relative size of the particle shadows, δ. In the first model considered, our calculations are based on the moments of the transparency T in that part of the ring A sampled by the occultation, thus extending the work of  Showalter and Nicholson (1990) to larger τ  and δ, and to higher central moments, without their simplifying assumptions. We also calculate these statistics using an approach based on the autocovariance, autocoskewness and autocokurtosis.

These new approaches compare well to the formula for excess variance from Showalter and Nicholson in the region where all are accurate, δτ≪1. Skewness for small τ has a different sign for transparent and opaque structures, distinguishing gaps from clumps. The higher order central moments are more sensitive to the extremes of the size distribution and opacity.

We explain the upward curvature of the dependence of normalized excess variance for Saturn’s background C ring by the observation of Jerousek etal (2018) that the measured optical depth is correlated with particle size. For a linear dependence R_eff = 12 * (τ – 0.08) + 1.8m from Jerousek’s results, we match the curvature of normalized excess variance, the skewness and the kurtosis in the region between 78,000 and 84,600km from Saturn.

Statistics calculated from the granola bar model give different predictions from individual particles. The different τ dependence suggests that the wave crests compress the gaps more than the wakes, and produce more regularity among the clumps; and larger and more opaque self-gravity wakes in the wave crests, with transparent ghosts. The UVIS observations fall between the most regular and the most irregular granola bar models.

We compare selected occultations (Eckert etal 2020) at different values of the elevation B to estimate the flattening and axial ratio of ring particles and clumps. In Ring C, we find spheres: The statistical measures from multiple occultations follow the expected dependence on sin B, e.g. Showalter & Nicholson (1990). However, in the Janus 2:1 and Mimas 5:3 density waves, the excess variance for stars β Cen, λ Sco and σ Sgr shows no B dependence. This is exactly the expectation for completely flat (H/W =0) self-gravity wakes that we have derived from the autocovariance of the wake shadows. A closer analysis of this particular case gives H/W < 0.04, different from Colwell etal (2007), suggesting wakes are more like linguine than granola bars.

How to cite: Esposito, L. W., Sremcevic, M., Colwell, J., Eckert, S., and Jerousek, R.: Flattening of ring particles and self-gravity wakes in Saturn’s rings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3519, https://doi.org/10.5194/egusphere-egu21-3519, 2021.

The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander successfully delivered a geophysical instrument package to the Martian surface on November 26, 2018, including a broadband seismometer called SEIS (Seismic Experiment for Interior Structure). After two years of recording, seismic body waves phases of a small number of high-quality marsquakes have been clearly identified. In this work, we will present how we estimate the body waves arrival times, and how we handle them to constrain the locations of the marsquakes and the interior structure. The inverse problem relies on a Bayesian approach, to investigate a large range of possible locations and interior models. Due to the small number of data, the advantage of using such a method is to provide a quantitative measure of the uncertainties and the non-uniqueness. In order to take into account the strong variations of the crustal thickness due to the crustal dichotomy, and thus consider the seismic lateral variations, which could cause significant misinterpretations, arrival times corrections are added using crustal thickness maps obtained from gravity and topography data.

How to cite: Drilleau, M., Garcia, R., Samuel, H., Rivoldini, A., Wieczorek, M., Lognonné, P., Panning, M., Perrin, C., Ceylan, S., Schmerr, N., Khan, A., Lekic, V., Stähler, S., Giardini, D., Kim, D., Huang, Q., Clinton, J., Kawamura, T., Scholz, J.-R., and Davis, P. and the InSight Science Team: Estimation of the marsquakes’ location and the interior structure of Mars using InSight data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14998, https://doi.org/10.5194/egusphere-egu21-14998, 2021.

The InSight seismometer SEIS recorded tens of high-frequency (1.5-5Hz; HF) and Very-high frequency (1.5-15Hz, VF) Martian events. They are characterized by two temporally separated arrivals with a gradual beginning, a broad maximum and a very long decay. This observation is consistent with a long-range propagation of seismic P and S waves in a heterogeneous crust (Van Driel et al., accepted). To examine this hypothesis, first, we employ basic multiple-scattering concepts on the two groups of events. Then, we propose a full envelope modeling based on elastic radiative transport in a half-space. The model parametrization and the radiative transfer equations are presented in (Lognonné, P., et al. (2020) and Margerin, L., (2017)). We find that both HF and VF signals are depolarized and verify Gaussian statistics, at the exception of the ballistic primary and secondary arrivals. These properties agree with a multiple-scattering origin. For VF events, the energy partitioning ratio V²/H² between horizontal and vertical components is frequency dependent. We observe that V²/H² is maximum at the so-called ‘2.4Hz resonance’ (~2) and decreases rapidly at frequencies higher than 5Hz (~0.1) then i remains relatively low up to frequencies of 15Hz at least. HF events do not exhibit a decrease of V²/H² at high frequencies however further analysis reveals a strong correlation between energy partitioning and signal-to-noise (S/N) ratio for HF events. This observation suggests that a part of the difference between the HF and VF events can to some extent be explained by noise contamination. The generally low V²/H² ratio of VF events is reminiscent of the response of unconsolidated layers, as observed at Pinyon Flats Observatory on Earth (Margerin, L., et al. (2009)). Unlike earthquakes and moonquakes observed in the same frequency band, the delay time measured from onset to peak of the secondary arrival of HF and VF events is frequency-independent. This suggests that the spectrum of heterogeneity of the Martian crust is smooth. We observe that, for HF and VF events, the delay time is weakly dependent on hypocentral distance. This observation cannot be reconciled with the predictions of multiple-scattering theories in a statistically homogeneous medium however it suggests a stratification of heterogeneity in the Martian lithosphere. The coda quality factor Q_c of VF events is high and shows a linear increase with frequency. Q_c of HF events is higher but it may be overestimated due to the noise contamination. The linear frequency dependence of Q_c is strongly reminiscent of the leakage effect in a crustal scattering waveguide and suggests that part of the observed coda attenuation may be of structural origin. The full envelope modeling of the S0334a VF event results shows that the estimated value of the diffusivity (≃ 619 km²/s) is almost 6 times greater than for the S0128a VF event (≃ 90 km²/s). This observation again suggests a stratification of heterogeneity. In future works, we will perform the full envelope modeling of all the VF selected events at different frequencies to constrain a 1D attenuation and diffusion model of the Martian crust.

How to cite: Menina, S., Margerin, L., Kawamura, T., Lognonné, P., Marti, J., Drilleau, M., Calvet, M., Schmerr, N., van Driel, M., and Karakostas, F.: Energetic characteristics of High Frequency (HF) and Very High Frequency (VF) Martian events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14609, https://doi.org/10.5194/egusphere-egu21-14609, 2021.

HEND (High Energy Neutron Detector) onboard NASA’s Mars Odyssey spacecraft performs measurements of neutron emission of Martian surface 2002. HEND uses ³He counters for detection of epithermal neutrons generated by Galaсtic Cosmic Rays interaction with surface and atmosphere of Mars.

Weak Martian atmosphere emits, absorbs and scatters neutrons slightly, and outgoing neutron flux on the orbit is changing depending on atmospheric density along the Martian seasons. We have analyzed the HEND data for seasonal variations of outgoing neutron flux above several areas of Mars for nine Martian annual cycles. Measured seasonal variations, presented as Ls profiles for individual years, are compared with numerically predicted profiles according to the model of Martian atmosphere.

How to cite: Golovin, D., Mitrofanov, I., Litvak, M., Sanin, A., and Malakhov, A.: Annual variations of Mars atmosphere, as seen by HEND data since 2002, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11879, https://doi.org/10.5194/egusphere-egu21-11879, 2021.

The electron density (N_e) profiles over the northern high-latitude region measured with Radio Occultation Science Experiments (ROSE) onboard the Mars Atmosphere and Volatile Evolution (MAVEN) have indicated more complicated ionospheric structure of Mars than previously thought.  Some of the profiles have shown wide and narrow shapes of the main N_e peaks, while others show anomalous characteristics of the topside plasma distribution.  Large variations in the topside N_e scale heights are observed presumably in response to the outward flow of ionospheric plasma or changes in plasma temperatures.   We use our 1-D chemical diffusive model coupled with the Mars - Global Ionosphere Thermosphere Model (M-GITM) to interpret these N_e profiles.  Our model is a coupled finite difference primitive equation model which solves for plasma densities and vertical ion fluxes.  The photochemical equilibrium in the model for each ion is assumed at the lower boundary, while the flux boundary condition is assumed at the upper boundary to simulate plasma loss from the Martian ionosphere.  The crustal magnetic field at the measured N_e locations is weak and mainly horizontal and does not allow plasma to move vertically.   Thus, the primary plasma loss from the topside ionosphere at these locations is most likely caused by diverging horizontal fluxes of ions, indicating that the dynamics of the upper ionosphere of Mars is controlled by the solar wind.  The primary source of ionization in the model is due to solar EUV radiation.  We find that the variation in the topside N_e scale heights is sensitive to magnitudes of upward ion fluxes derived from ion velocities that we impose at the upper boundary to explain the topside ionospheric structure.  The model requires upward velocities ranging from 60 ms^-1 to 80 ms^-1 for all ions to ensure an agreement with the measured N_e profiles. The corresponding outward fluxes in the range 1.6 x 10⁶ – 3.8 x 10⁶ cm^-2 s^-1 are calculated for O₂⁺ compared to those for O⁺ in the range 4 x 105 – 6 x 105 cm^-2 s^-1.  The model results for the northern N_e profiles will be presented in comparison with the measured N_e profiles.  This work is supported by Mohammed Bin Rashid Space Centre (MBRSC), Dubai, UAE, under Grant ID number 201604.MA.AUS.

How to cite: Majeed, T., Al-Mutawa, S., and Bougher, S.: A Model Analysis of the MAVEN/ROSE Electron Density Profiles at Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6555, https://doi.org/10.5194/egusphere-egu21-6555, 2021.

Several detections of methane in the Martian atmosphere have been reported from Earth-based and Mars orbit instruments with abundances ranging up to tens of ppbv, while in-situ measurements performed by the MSL rover at Gale crater showed some peaks up to 7 ppbv. A variety of methane formation mechanisms occurring in the subsurface have been proposed such as abiotic synthesis through Fischer-Tropsch Type (FTT) reactions. After its generation at depth, Martian methane can migrate upwards and be either directly released at the surface or trapped in subsurface reservoirs, such as clathrate hydrates, where it could accumulate over long time before being episodically liberated during destabilizing events. When ascending through stratigraphic layers, methane can move via one or several transport mechanisms. Seepage can occur through advection, the main CH₄ transport process on Earth, driven by pressure gradients and permeability and generally associated to fracture networks. Another transport mechanism is diffusion, which is mainly controlled by concentration gradient. This process is not efficient on short timescales and short-lived methane plumes related to diffusion should therefore originate from very shallow depths.

In this work, we model the subsurface transport of methane on Mars and its subsequent trapping in clathrate hydrates. For the latter, the effect of the clathrate formation pressure is especially examined, while methane subsurface transport is studied considering adsorption onto, advection and diffusion through the regolith.

How to cite: Gloesener, E., Karatekin, Ö., and Dehant, V.: Migration and storage of methane in the Martian crust , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15495, https://doi.org/10.5194/egusphere-egu21-15495, 2021.

Photoanalytical segmentation of individual soil grains and granulometry in high-resolution surface images are key in understanding sedimentation processes of planetary bodies before samples return to Earth. Here we present a Mathematica-based semi-automated image segmenting software tool that allows fast segmentation and granulometry analysis of Martian (soil) images based on the algorithm of Karunatillake et al. (2013, 2014), with a graphical user interface (GUI) to increase the software accessibility.

Our software has been adapted to Martian in-situ observation images including the Mars Hand Lens Imager (MAHLI) and Microscopic Imager (MI), providing segmenting and granulometry measurement through steps below: (1) Image imported: all common raster images are supported, as well as the IMG formatted MAHLI and MI images. While the MI image possesses a constant pixel size of 31 μm/pixel, for MAHLI images with various focal lengths, a focus motor count is required to calculate pixel size. The imported images are processed with gamma correction, contrast adjustment, background sharpen, and are visually decided whether there is a distinct foreground before going to the second step: (2) Image segmented: two independent modules are designed for segmenting the foreground and background with separate parameters, the coarser-grained foreground was masked before the finer-grained background is segmented. The GUI allows dynamic visualization of how the segmenting result changes with each parameter, facilitating the setting of parameters. (3) Granulometry: the grain size is calculated from the focal length and Wentworth classification of detected grains is established, highlighting the dominant class of grain size. The probability density and cumulative distribution of grain size can also be plotted. The granulometry results and parameters used are supported to export.

To check the performance of our software, we qualitatively tested our software with 57 MAHLI and MI images with or without foreground, with comparison to region based segmentation method such as BASEGRAIN, edge detection based method such as ENVI Classification tools and Feature Extraction tools, and supervised segmentation methods such as ENVI supervised classification tools and ImageJ Trainable Weka Segmentation tool. Our software shows better results in generating grains with closed boundaries and distinguishing adjacent grains with similar colors, with the fastest speed and less workload. Factors that may influence the accuracy of segmenting include image resolution, camera angle, inter-grain brightness/color contrast and shadow coverage.

In future work, a particle morphometry measuring function will be added so that statistics of grain roundness, sphericity, and angularity could be obtained. High-resolution images from the Moon and the asteroids will also be used in software testing to expand the range of its applicability to other planetary bodies. We will also consider its application on terrestrial cases, such as images of terrestrial sediments or petrological thin sections, which will need further improvement of the software concerning the increased compositional and optical complexity of terrestrial grains.

How to cite: Shi, Y., Zhao, S., Karunatillake, S., and Xiao, L.: Semi-automated Image Segmenting Software for Martian Soil Granulometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7872, https://doi.org/10.5194/egusphere-egu21-7872, 2021.

On Earth, jarosite is a weathering product forming in acidic-oxidative environments from the alteration of iron-bearing minerals in presence of liquid water. Typical settings where this iron-potassium hydrated sulphate is found, are weathering zones of pyrite-rich deposits, evaporative basins and fumaroles. Jarosite is not only known on Earth, it also occurs on Mars, where it was firstly identified by the Opportunity rover. The mineral was in fact recognized in the finely layered formations outcropping at Meridiani Planum and that were accurately investigated by the rover (Klingelhöfer et al. 2004). Since jarosite requires liquid water to form, its occurrence on Mars has been regarded as an evidence for the presence of liquid water in the geologic past of Mars (Elwood-Madden et al., 2004). Since then, many models have been proposed to describe the environments where the precipitation of Martian jarosite took place. The most accepted ones deal with evaporative basins similar to Earth’s playas, others concern volcanic activity and hydrothermal processes. An alternative proposal predicted that jarosite may have formed as a consequence of weathering of mineral dust trapped in massive ice deposits, i.e. the ice-weathering model (Niles & Michalsky, 2009). The hypothesis that jarosite formed on Mars because of low-temperature, acidic and water limited weathering, is not new (Burns, 1987), but until now no direct evidences were available to support it.

A potential Earth analogue to investigate such processes is deep Antarctic ice. We present a first investigation of deep ice samples from the Talos Dome ice core (East Antarctica) aimed at the identification of englacial jarosite, so as to support the ice-weathering model. Evidences gathered through independent techniques showed that jarosite is actually present in deep Antarctic ice and results from the weathering of dust trapped into ice. The process is controlled by the re-crystallization of ice grains and the concurrent re-location of impurities at grain-junctions, which both depend on ice depth. This study demonstrates that the deep englacial environment is suitable for jarosite precipitation. Our findings support the hypothesis that, as originally predicted by the ice-weathering model, paleo ice-related processes have been important in the geologic and geochemical history of Mars.

References

Burns, R. Ferric sulfates on Mars. J. Geophys. Res. 92, E570-E574 (1987).

Elwood-Madden et al., 2004. Jarosite as an indicator of water-limited chemical weathering on Mars. Nature 431, 821-823 (2004).

Klingelhöfer, G. et al. Jarosite and Hematite at Meridiani Planum from Opportunity's Mössbauer Spectrometer. Science 306, 1740-1745 (2004).

Niles, P. B. & Michalski, J. M. Meridiani Planum sediments on Mars formed through weathering in massive ice deposits. Nat. Geosci. 2, 215-220 (2009).

How to cite: Baccolo, G., Delmonte, B., Niles, P., Cibin, G., Di Stefano, E., Hampai, D., Keller, L., Maggi, V., Marcelli, A., Michalski, J., Snead, C., and Frezzotti, M.: Jarosite in Antarctic deep ice supports the ice-weathering model for jarosite formation on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6279, https://doi.org/10.5194/egusphere-egu21-6279, 2021.

This work presents the latest results on the estimations of Water Equivalent Hydrogen (WEH) gathered in martian areas Vera Rubin ridge (VRR) and Glen Torridon (GT) by the Dynamic Albedo of Neutron (DAN) instrument installed onboard NASA’s Curiosity rover. The main science objective of DAN is to study bound water content in shallow layer of martian subsurface down to 0.6 m [1].

Extensive scientific campaign on Vera Rubin ridge was started in the middle of 2017 and lasted until the beginning of 2019 when the rover reached another region – Glen Torridon. VRR is mostly related to hematite minerals that might be formed in the presence of liquid water. On the other hand, GT region is thought to be associated with clay minerals, according to CRISM observations [2].

We will present the latest results on DAN passive observations in these Mars areas. Data are referred to the period of more than 3 years of observations or MSL traverse segment from 17 km to 23 km. The main result is the notable increase of WEH in GT in comparison with VRR, as well as in comparison with the whole Curiosity traverse. Possibly, the increase may indicate on the qualitative difference in neutron-absorption elements that are forming the soil of the GT region.

References:

[1] Mitrofanov, I. G., et al., (2014). Water and chlorine content in the Martian soil along the first 1900 m of the Curiosity rover traverse as estimated by the DAN instrument. J. Geophys. Res., 119(7), 1579–1596. doi:10.1002/2013JE004553.

[2] Murchie, S. L., et al. (2009), Compact Reconnaissance Imaging Spectrometer for Mars investigation and data set from the Mars Reconnaissance Orbiter's primary science phase, J. Geophys. Res., 114, E00D07, doi:10.1029/2009JE003344.

How to cite: Nikiforov, S., Djachkova, M., Mitrofanov, I., Litvak, M., Lisov, D., and Sanin, A.: Estimation of Water Content in Vera Rubin Ridge and Glen Torridon areas Based on Measurements of the MSL/DAN Instrument in Gale crater, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11196, https://doi.org/10.5194/egusphere-egu21-11196, 2021.

Current knowledge of the clay unit at Oxia Planum, the Rosalind Franklin rovers landing site, is based in large part on spectroscopy data from the OMEGA and CRISM instruments. While these instruments have proved useful for creating a broad map of this unit, along with identifying candidates for the clay making up the unit, their usefulness is limited by their spatial resolution. Mapping at Oxia has primarily been carried out using 1200-300m/pixel OMEGA or 200-100m/pixel CRISM data and, even accounting for the intermittent 18m/pixel CRISM hyperspectral data available, existing clay maps are insufficient for the purposes of rover traverse planning.

Images from the Colour and Stereo Surface Imaging System¹ (CaSSIS), which has a resolution of 4m/pixel, can improve upon this. Work done by members of the CaSSIS science team identified certain CaSSIS band ratios which can aid in identifying the presence of ferric/ferrous minerals². In a more recent study CRISM, HiRISE colour and CaSSIS data were used to identify that at least two spectrally and morphologically distinct subunits make up the Oxia clay unit³. These sub units are divided into a lower and upper member. The lower member appears orange in CaSSIS/HiRISE VNIR images, shows extensive metre-scale fracturing and possesses CRISM spectral signatures consistent with the presence of a Fe/Mg-rich clay mineral. The upper member, blue in CaSSIS/HiRISE VNIR images, shows metre-decametre scale fracturing along with CRISM spectral signatures consistent with a mix of a Fe/Mg-rich clay mineral and olivine.

This work demonstrates that ferric detections within CaSSIS band ratios correlate well with CRISM, and that the lower clay member appears to have a higher ferric content than the upper member. Given this a new, higher resolution clay map is being created using CaSSIS band ratios in conjunction with HiRISE greyscale imagery to observe fracture size. This map, currently being constructed over the 1-sigma landing ellipses, delineates between the two subunits well in addition to revealing those areas where the two subunits are too intermixed to reliably differentiate at CaSSIS’s resolution. Given that CaSSIS has higher resolution in comparison to the CRISM/OMEGA instruments, that it can differentiate between the clay sub-units, and that it provides higher landing site coverage compared to CRISM hyperspectral data, means this map will provide a significant improvement over what is currently available for the sites clay unit.

References; 1; Thomas N. et al. (2017). "The Colour and Stereo Surface Imaging System (CaSSIS) for the ExoMars Trace Gas Orbiter." Space Science Reviews 212(3-4): 1897-1944. 2; Tornabene L. L. et al. (2017). "Image Simulation and Assessment of the Colour and Spatial Capabilities of the Colour and Stereo Surface Imaging System (CaSSIS) on the ExoMars Trace Gas Orbiter." Space Science Reviews 214(1). 3; Mandon L. et al. (in review). "Spectral Diversity and Stratigraphy of the Clay-Bearing Unit at the Exomars 2020 Landing Site Oxia Planum." Astrobiology

Acknowledgement; CaSSIS is a project of the University of Bern, with instrument hardware development supported by INAF/Astronomical Observatory of Padova (ASI-INAF agreement n.2020-17-HH.0), and the Space Research Center (CBK) in Warsaw.

How to cite: Parkes Bowen, A., Mandon, L., Bridges, J., Quantin-Nataf, C., Tornabene, L., Briggs, J., Thomas, N., and Cremonese, G.: Mapping and characterisation of the Oxia Planum clay-bearing unit using CaSSIS imagery, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13356, https://doi.org/10.5194/egusphere-egu21-13356, 2021.

Pit craters are enigmatic sub-circular depressions observed on rocky and icy planetary bodies across the Solar System. These craters do not primarily form during catastrophic impact or the forcible eruption of subsurface materials, but likely due to collapse of subsurface cavities following fluid (e.g., magma) movement and/or extensional tectonics. Pit craters thus provide important surficial records of otherwise inaccessible subsurface processes. However, unlocking these pit crater archives is difficult because we do not know how their surface expression relates to their subsurface structure or driving mechanisms. As such, there is a variety of hypotheses concerning pit crater formation, which variously relate cavity collapse to: (i) opening of dilatational jogs during faulting; (ii) tensile fracturing; (iii) karst development; (iv) permafrost melting; (v) lava tube evacuation; (vi) volatile release from dyke tip process zones; (vii) pressure waning behind a propagating dike tip; (viii) migration of magma away from a reservoir; and/or (ix) hydrothermal fluid movement inducing host rock porosity collapse. Validating whether these proposed mechanisms can drive pit crater formation and, if so, identifying how the physical characteristics of pits can be used to infer their driving mechanisms, is critical to probing subsurface processes on Earth and other planetary bodies.

Here we use seismic reflection data from the North Carnarvon Basin offshore NW Australia, which provides ultra-sound like images of Earth’s subsurface, to characterize the subsurface structure of natural pit craters. We extracted geometrical data for 61 pits, and find that they are broadly cylindrical, with some displaying an inverted conical (trumpet-like) morphology at their tops. Fifty-six pit craters, which are sub-circular and have widths of ~150–740 m, extend down ~500 m to and are aligned in chains above the upper tips of dikes; crater depths are  ~12–225 m. These dike-related pit craters occur within long, linear graben interpreted to be bound by dyke-induced normal faults. Five pit craters, which are ~140–740 m wide and ~32–107 m deep, formed independent of dykes and are associated only with tectonic normal faults. Our preliminary data reveal a moderate, positive correlation between crater width and depth but there is no distinction between the depth and width trends of pit craters associated with dikes and those with tectonic normal faults. To test whether our quantitative data can be used to inform interpretation of pit craters observed on other planetary bodies, we compare their morphology to those imaged in Noctis Labyrinthus on Mars; there are >200 pit craters here, most of which occur in chains, with widths ranging from 369–11743 m and depths from 1–1858 m.

Overall, we show reflection seismology is a powerful tool for studying the three-dimensional geometry of pit craters, with which we can test pit crater formation mechanisms. We anticipate future seismic-based studies will improve our understanding of how the surface expressions of pit craters (either in subaerial or submarine settings) can be used to reconstruct subsurface structures and processes on other planetary bodies, where such subsurface information is not currently available.

How to cite: Magee, C., Jackson, C. A.-L., Kling, C. L., and Byrne, P. K.: Imaging the subsurface structure of pit craters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5067, https://doi.org/10.5194/egusphere-egu21-5067, 2021.

The North Polar Layered Deposits (NPLD), which consist of dusty water ice layers, have recorded the climatic variations of Mars. We use High Resolution Imaging Science Experiment (HiRISE) data (ground pixel size of up to ~0.25m/pixel) to study the morphology and current erosional processes at the NPLD scarps. Fanara et al. (1,2) have performed automated detection of the fallen ice blocks at the foot of scarps. Our aim is to search for their possible source areas.

We apply change detection techniques to multi-temporal images. The images are ortho-rectified using HiRISE Digital Terrain Model (DTM) and then co-registered to ensure subpixel alignment accuracy. Due to the low-sun conditions in Martian polar areas, the surface morphology can be revealed from cast shadows. In addition, HiRISE operates on a nearly sun-synchronous orbit, which means the images are taken at the same local time of day, providing good conditions for automatically detecting changes in shadow patterns of the ice-fragments.

The areas with changed shadows illustrate the spatial distribution of mass wasting activities. Our results show that most of the detached ice-fragments originate from the lower parts of the scarp, which are heavily affected by fracturing. Based on the detected changes, we will further investigate the characteristics of mass wasting and estimate the volume of the detached ice-fragments. The temporal and spatial distribution of detached ice fragments at different NPLD scarps can provide insights into the ice behavior and thus support modelling studies of viscous flow velocities (3), thermoelastic stresses (4) and climate variations of Mars. Ultimately, we intend to explore the evolution of the NPLD scarps by correlating long-term mass wasting characteristics with seasonal and morphological parameters.

References

[1] Fanara et al.,2020. Planetary and Space Science. 180, p.104733.

[2] Fanara et al.,2020. Icarus. 342, p.113434.

[3] Sori et al., 2016. Geophysical Research Letters, 43(2), pp.541-549.

[4] Byrne et al., 2017. EPSC, Vol. 11.

How to cite: Su, S., Fanara, L., Zhang, X., Gwinner, K., Hauber, E., and Oberst, J.: Sources of ice block falls at the Martian north polar scarps: detection from multi-temporal HiRISE image sets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7489, https://doi.org/10.5194/egusphere-egu21-7489, 2021.

       There are thousands of small cones on Isidis Planitia on Mars. The cones have diameters of 300–500 m and heights of ~30 m. Many cones form subparallel chains several kilometers in length. Their origin is discussed in many papers [1,2,3,4] however, the mechanism of their formation is not explained, nor the reason for their arrangement in subparallel chains. The cones may be: rootless cones, cinder cones, tuff cones, pingos, mud volcanoes etc. [4]. Some of chains have a characteristic furrow suggesting possibility of fissure volcanism.

       The prevalence of these chains indicates that large-scale processes are responsible for their formation. Their proper classification can help identify their origin and explain other large-scale processes on Isidis Planitia. There are a few works about statistics of cones  on Isidis Planitia e.g. [1,2,5]. However, we approached the problem in a different way. 

        Our analysis indicates that the cones can be grouped in larger systems. We divided Isidis Planitia into several characteristic regions. There may be several types of cones in one of the distinguished regions. Our division is based on the following structures:

1.Chains of separate cones,

2.Chains of cones connected with each other,

3a. Chains of cones connected to the furrow through the center,

3b. Chains of cones connected to the furrow through the center with elongated, elliptical cones,

4. Chains of cones with the traces of flows,

5. Chains of irregular cones without calderas with a depression around the cones,

6a. Ridge arches without cones,

6b. Chains of cones on the ridges. 

        We also paid attention to the orientation of the chains of cones. In most of our regions there are also groups of cones that do not form linear chains. Such group are named as "field of cones''

         Our current Isidis Planitia division includes 36 regions. We distinguished 11 regions with the predominant arrangement of arcs in the directions between ENE and ESE, 5 regions with the directions between WNW and WSW, 2 regions with the directions between NNE and NNW and 15 areas with the directions between SSE and SSW, 3 areas where the arcs of the cones form circles. In the rest of our regions there are no chains of cones.  

       We marked also sinuous ridges, cracks and serial depressions, occurring near craters, fields with polygonally cracked surface and quasi-circular depressions sQCDs - ghost craters [4].

Plan of future research: The next stage of our research is to explain the origin of the formation of each type of cone and their chains on Isidis Planitia.

References:

[1] Guidat, T., et al., (2015) Earth and Planet. Sci. Let . 411, 253-267. [2] Souček, O., et al., (2015) Earth and Planet. Sci. Let 426, 176-190.  [3] Gallinger, C.L. and Ghent, R. R., (2016) 40th Lunar and Planet. Sci. Conf. 1953. [4] Ghent, R. R., et al., (2012) Icarus 217, 1169-183. [5] Hiesinger H., et al., (2009)  47th Lunar and Planet. Sci. Conf. 2767.

How to cite: Zalewska, N., Czechowski, L., Ciążela, J., and Kuzaj, M.: Regional morphological division on Isidis Planitia on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13700, https://doi.org/10.5194/egusphere-egu21-13700, 2021.

Dynamic changes of Martian north polar scarps present a valuable insight into the planet's natural climate cycles (Byrne, 2009; Head et al., 2003)^1,2. Annual avalanches and block falls are amongst the most noticeable surface processes that can be directly linked with the extent of the latter dynamics (Fanara et al, 2020)³. New remote sensing approaches based on machine learning allow us to make precise records of the aforementioned mass wasting activity by automatically extracting and analyzing bulk information obtained from satellite imagery.  Previous studies have concluded that a Support Vector Machine (SVM) classifier trained using Histograms of Oriented Gradients (HOG) can be used to efficiently detect block falls, even against backgrounds with increased complexity (Fanara et al., 2020)⁴. We hypothesise that this pretrained model can now be utilized to generate an extended dataset of labelled image data, sufficient in size to opt for a deep learning approach. On top of improving the detection model we also attempt to address the image co-registration protocol. Prior research has suggested this to be a substantial bottleneck, which reduces the amounts of suitable images. We plan to overcome these limitations either by extending our model to include multi-sensor data, or by deploying improved methods designed for exclusively optical data (e.g.  COSI-CORR software (Ayoub, Leprince and Avouac, 2017)⁵).  The resulting algorithm should be a robust solution capable of improving on the already established baselines of 75.1% and 8.5% for TPR and FDR respectively (Fanara et al., 2020)4. The NPLD is our primary area of interest due to it’s high levels of activity and good satellite image density, yet we also plan to apply our pipeline to different surface changes and Martian regions as well as on other celestial objects.

1. Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003. Recent ice ages on Mars. Nature 426, 797–802

2. Byrne, S., 2009. The polar deposits of Mars. Annu. Rev. Earth Planet. Sci. 37, 535–560.

3. Fanara, K. Gwinner, E. Hauber, J. Oberst, Present-day erosion rate of north polar scarps on Mars due to active mass wasting; Icarus,Volume 342, 2020; 113434, ISSN 0019-1035.

4. Fanara, K. Gwinner, E. Hauber, J. Oberst, Automated detection of block falls in the north polar region of Mars; Planetary and Space Science, Volume 180, 2020; 104733, ISSN 0032-0633.

5. Ayoub, F.; Leprince, S.; Avouac, J.-P. User’s Guide to COSI-CORR Co-registration of Optically Sensed Images and Correlation; California Institute of Technology: Pasadena, CA, USA, 2009; pp. 1–49.

How to cite: Martynchuk, O., Fanara, L., Hauber, E., Oberst, J., and Gwinner, K.: Computer vision model for detecting block falls at the martian north polar region., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15776, https://doi.org/10.5194/egusphere-egu21-15776, 2021.